1. Field of the Invention
The invention relates to the field of telephonic communication and, in particular, to hands-free operation wherein a speaker phone is utilized.
2. Description of the Prior Art
Conventional telephonic conversations occur through telephone handsets or headsets wherein the audio transmitter and audio receiver are acoustically decoupled. In the case of a conventional telephone handset, the acoustical coupling between the earpiece and mouthpiece, given the respective audio volumes produced at the earpiece or mouthpiece, are such that the amount of feedback introduced into the communicational loop is de minimis. In other words, in a conventional handset the audio volume received at the earpiece is not picked up at the mouthpiece at a magnitude great enough to form an interfering feedback loop in the two-way telephone conversation. In the case of a conventional headset, the acoustical separation between the earpiece and mouthpiece is even greater since the earpiece generally is tightly fitted to the wearer's ear and connected to the mouthpiece only through a thin plastic tube.
However, in the case of a hands-free or speaker phone operation, the audio signal intensity produced by the speaker is generally within the same order of magnitude as the audio signals produced by the user at the microphone pick-up. This is true even in the case where the speaker and microphone are physically separable, since the intensity of the audio signal from the speaker must be great enough to be easily heard by the user, and the microphone must be sensitive enough to pick up audio signals at reasonable audio voice levels. In order to avoid the inherent feedback which would otherwise occur, hands-free speakers contain automatic voice muting circuitry. Thus, when an audio signal is being produced at the speaker, the microphone is disabled. In addition, in some units, if an audio signal beyond a predetermined threshold is picked up at the microphone from the user, the audio signal to the speaker is cut off. Therefore, it is generally impossible in an hands-free operation to have any degree of overlap in conversations. Furthermore, the switchover or muting operation generally takes a few tenths of seconds to operate, which makes rapid interchange of conversation between the caller and receiver difficult.
More significantly, the use of hands-free operation must occur in a relatively quiet environment. Any background noise of significant magnitude will serve to activate the muting operation, thereby substantially interfering with, or disabling, the conversation of one of the parties. Hands-free speaker phone operation cannot therefore be used in noisy environments.
What is needed then is some means whereby hands-free operation of a telephone may be practiced in a noisy environment wherein loud distant noises can be distinguished from closer sounds, such as the speaker's voice.